1. Field of the Invention
The present invention relates to a taking lens apparatus. More specifically, the present invention relates to a taking lens apparatus (a main component of a digital still camera, digital video camera, or camera incorporated in or externally fitted to a personal computer, mobile computer, cellular phone, personal digital assistant (PDA), or the like) that optically takes in an image of a subject through an optical system and that then outputs it in the form of an electrical signal by means of an image sensor, and in particular to a taking lens apparatus provided with a compact zoom lens system. The present invention also relates to a slim camera provided with such a taking lens apparatus.
2. Description of the Prior Art
In recent years, as personal computers and the like become increasingly wide-spread, digital still cameras and digital video cameras (hereinafter collectively referred to as digital cameras), which permit easy capturing of images into digital equipment, have been becoming increasingly popular with individual users. Digital cameras are expected to continue becoming more and more popular into the future as an image data input device. The image quality of a digital camera generally depends on the number of pixels provided on a solid-state image sensor, such as a CCD (charge-coupled device). Nowadays, digital cameras for general consumers boast of high resolution over one mega pixels, and are closing in on cameras using silver-halide film in image quality. Accordingly, to cope with high resolution of modern image sensors, high optical performance is sought in taking lens systems.
Moreover, in digital cameras for general consumers, while zooming, in particular optical zooming with minimal image degradation, is desired, slimness is also required for better portability. Accordingly, to cope with increasingly high image quality and increasing slimness in digital cameras, various types of zoom lens systems have conventionally been proposed, for example in the following publications:
Document 1: U.S. Pat. No. 6,498,687
Document 2: Japanese Patent Application Laid-Open No. 2000-137164
Document 3: Japanese Patent Application Laid-Open No. H8-248318
Document 4: U.S. Pat. No. 6,104,432
Document 5: United States Patent Application Published No. 2002/0136150 A1
Document 6: Japanese Patent Application Laid-Open No. H11-258678
In conventionally proposed zoom lens systems for digital cameras, the most common way to make a digital camera slim is to adopt a so-called collapsible lens barrel. In a zoom lens system adopting a collapsible lens barrel, when the camera is not used, the zoom lens system collapses so that its lens elements are held with minimum distances between them, and, when the camera is used, the zoom lens system moves out so that its lens elements are held in a duly arranged state. The zoom lens system disclosed in Document 1 attempts to reduce its thickness in its collapsed state by reducing the number of constituent lens elements while maintaining satisfactory optical performance. However, with a construction adopting a collapsible lens barrel, it is not possible to reduce the thickness of the zoom lens system to less than the total of the thickness of the lens elements themselves, that of the image sensor, and that of the optical filter and other components required by the image sensor. This makes it impossible to make the digital camera satisfactorily slim.
Another way to make a digital camera slim is to ingeniously arranging a zoom lens system inside the camera. In common digital cameras, a zoom lens system is arranged with the largest surface of its housing facing the subject. Arranging the zoom lens system in this way, however, results in the length of the zoom lens system greatly affecting the thickness of the digital camera. This can be overcome by arranging a zoom lens system, like the one disclosed in Document 2, with its optical axis parallel to the largest surface of its housing. This prevents the thickness of the digital camera from being affected by the length of the zoom lens system, and thus helps make the digital camera slim. This construction, however, makes the camera elongate, and thus makes the camera extremely difficult to use. Usability may be improved by rotatably fitting the lens barrel so that the lens barrel is rotated when the camera is used. This, however, additionally requires a mechanism for rotating the lens barrel, and thus eventually increases the thickness of the digital camera. Moreover, extra operations are required to rotate the lens barrel at the start and end of photographing. This is troublesome and is therefore undesirable.
As described above, making photographing possible with the largest surface of the housing of a zoom lens system facing the subject is one requirement for realizing a slim and easy-to-operate digital camera. Examples of optical constructions that meet this requirement are the zoom lens systems disclosed in Documents 3 to 6. The zoom lens systems disclosed in Documents 3 to 6 are all so constructed as to make the largest surface of their housing face the subject by bending the optical path with a prism or mirror inserted between lens elements. However, none of these zoom lens systems is so constructed as to make a digital camera satisfactorily slim.
For example, the zoom lens system disclosed in Document 3 has a zoom construction where the first lens unit has a positive optical power (a so-called positive-led zoom construction), and the zoom lens system disclosed in Document 4 has a zoom construction where the first lens unit is afocal. With these zoom constructions, it is difficult to achieve zooming with a small number of zoom components, and in fact they achieve zooming with as many as four zoom components. Using a large number of zoom components complicates the construction of the lens barrel, and thus enlarges the lens barrel as a whole including drive components. This makes it difficult to make a camera slim. The zoom lens system disclosed in Document 5 achieves zooming by deforming a mirror. The construction required to drive and control the mirror to be deformed makes it difficult to make a digital camera slim. The zoom lens system disclosed in Document 6 achieves zooming by moving a lens disposed on the object side of a mirror. This requires the lens to be moved perpendicularly to the largest surface of the housing of the zoom lens system, and thus makes it difficult to make a digital camera slim.